PAPER MACHINE DRYING APPARATUS
United States Patent 3778908
At least one dryer felt roll in a paper machine dryer section is of the variable crown type so that the pressure with which the roll bears against the dryer felt may be varied along the length of the roll. In this way, nonuniformities in felt tension caused by the deflection of other felt rolls in the dryer section may be compensated for, and more uniform drying of a paper web in the cross machine direction obtained as it is pressed against the dryer drums by the dryer felt.
US Patent References:
Paper drying means
Williams - August 1932 - 1873949
Adjustable crown roll
Hornbostel - December 1964 - 3161125
TABLE ROLL
Denoyer et al. - May 1969 - 3443295
Paper drying means
Williams - August 1932 - 1873949
Adjustable crown roll
Hornbostel - December 1964 - 3161125
TABLE ROLL
Denoyer et al. - May 1969 - 3443295
Application Number:
05/166400
Publication Date:
12/18/1973
Filing Date:
07/27/1971
View Patent Images:
Export Citation:
Assignee:
The Black Clawson Company (Hamilton, OH)
Primary Class:
International Classes:
D21F5/02; D21F5/00
Field of Search:
34/116 26/63 29/116AD,116 100/162R 226/192,194,195
Primary Examiner:
Myhre, Charles J.
Assistant Examiner:
Streule Jr., Theophil W.
Parent Case Data:
CROSS REFERENCE TO RELATED APPLICATION
This application is a continuation of application Ser No. 833,407, filed June 16, 1969 now abandoned, for PAPER MACHINE DRYING APPARATUS.
Claims:
What is claimed is
1. In a dryer section, including a set of rotatable dryer drums, an endless felt trained about a portion of the peripheries of said drums to maintain a web being dried in said dryer section in contact with said drums a series of intermediate felt rolls positioned within the loop of said endless felt and adjacent said drums to maintain said felt adjacent said drums, and additional felt rolls for conveying said felt from the last drum of said set to the first drum thereof, the improvement comprising:
2. The apparatus of claim 1 wherein:
3. The apparatus of claim 2 wherein said deflecting means comprise:
4. The apparatus of claim 1 wherein:
5. A dryer section comrpising:
6. The apparatus of claim 5 wherein said means for controlling the pressure between said felt and said one of said rollers comprises:
7. The apparatus of claim 6 wherein said means for bowing said one of said rollers comprises:
8. The apparatus of claim 5 wherein:
9. A dryer section comprising:
10. In a paper making machine drying section including a plurality of rolls, portions of which are wrapped by an endless felt having substantially transversely extending seam therein, the method of controlling felt tension transversely thereof comprising:
11. The method of claim 10 wherein said step of varying said pressure comprises:
12. In a dryer including a plurality of rolls, portions of which are wrapped by an endless felt, the method of drying an indefininte length web in said dryer to a substantially uniform moisture profile in the cross machine direction comprising the steps of:
13. The method of claim 12 wherein said step of varying said pressure comprises:
1. In a dryer section, including a set of rotatable dryer drums, an endless felt trained about a portion of the peripheries of said drums to maintain a web being dried in said dryer section in contact with said drums a series of intermediate felt rolls positioned within the loop of said endless felt and adjacent said drums to maintain said felt adjacent said drums, and additional felt rolls for conveying said felt from the last drum of said set to the first drum thereof, the improvement comprising:
2. The apparatus of claim 1 wherein:
3. The apparatus of claim 2 wherein said deflecting means comprise:
4. The apparatus of claim 1 wherein:
5. A dryer section comrpising:
6. The apparatus of claim 5 wherein said means for controlling the pressure between said felt and said one of said rollers comprises:
7. The apparatus of claim 6 wherein said means for bowing said one of said rollers comprises:
8. The apparatus of claim 5 wherein:
9. A dryer section comprising:
10. In a paper making machine drying section including a plurality of rolls, portions of which are wrapped by an endless felt having substantially transversely extending seam therein, the method of controlling felt tension transversely thereof comprising:
11. The method of claim 10 wherein said step of varying said pressure comprises:
12. In a dryer including a plurality of rolls, portions of which are wrapped by an endless felt, the method of drying an indefininte length web in said dryer to a substantially uniform moisture profile in the cross machine direction comprising the steps of:
13. The method of claim 12 wherein said step of varying said pressure comprises:
Description:
BACKGROUND OF THE INVENTION
Conventional practice in drying a web of newly formed paper is to convey the moisture-laden web through a series of presses where water is expressed from the web by pairs of pressure rolls, and then to pass the web through a dryer section comprised of a series of large diameter, steam-heated drums. The drums in the dryer section are generally arranged in two sets, with the axes of the drums of each set oriented in generally the same horizontal plane. The drums in one set are positioned beneath the drums in the other set with their axes offset with respect to the set above them, and the paper web is trained in serpentine fashion about the drums. In this manner the paper web is pressed against the surfaces of each of the heated drums and is in turn heated, causing moisture to be evaporated from the web.
To enhance the drying rate, an endless felt is usually associated with each set of drums to press the wet web against the surface of the drums. To some extent, the pressure with which the felt presses the wet web against the drum surfaces will determine the rate at which the web is dried. It will also be obvious that if the tension in the dryer felt is nonuniform in the cross machine direction, the pressure with which the wet web is pressed against the drum surfaces will also be nonuniform and result in a nonuniform moisture profile in the web.
SUMMARY OF THE INVENTION
It has been discovered that a major cause of uneven felt tension in the cross machine direction the deflection of the rolls guiding the dryer felt about the surfaces of the dryer drums. To compensate for deflection of the dryer felt rolls, the present invention provides means for varying the tension in the dryer felt in the cross machine direction by varying the pressure with which at least one of the dryer felt rolls bears against the inner surface of the felt. This is accomplished by flexing the roll relative to its axis.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a somewhat schematic view of a dryer section of a paper machine incorporating the present invention;
FIG. 2 is an elevational view with parts in section showing a variable crown roll which finds utility in the present invention; and
FIG. 3 is a plan view of a portion of the dryer felt showing the effect on the dryer felt seam of varying tension transversely of the felt.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
As seen in FIG. 1 of the drawings, a web of paper W, shown in phantom lines, is led from the last press 10 of a press section about a pair of rollers 11 and 12, and thence into the dryer section comprising a plurality of additional rollers and referenced in its entirety by the numeral 13. The dryer section 13 comprises an upper set 20 and a lower set 30 of large diameter, steam-heated drums with the axes of the drums of each set in substantially the same horizontal plane and with the axes of the drums in the lower set offset with respect to the axes of those in the upper set. In this way, as the web enters the dryer section, it may be trained around each of the drums in serpentine fashion. To press the web W against the surfaces of the drums and to enhance heat transfer from the drums to the web, and hence the drying rate, a pair of endless felts 21 and 31 are provided, one for each set of drums in the dryer section.
The lower run of the upper felt 21 is maintained adjacent a portion of the peripheries of the upper set of drums 20 by means of a series of intermediate felt rolls 22, while lower felt 31 is maintained in position by means of the intermediate felt rolls 32. As the felts 21 and 31 leave the last drum in their respective sets, they are conveyed by means of turning rolls 23 and 33, respectively, a series of guide and stretch rolls, and lead in rolls 24 and 34, respectively, back into the dryer section.
As will be observed from FIG. 1, the felt rolls are of considerably less diameter than the dryer drums, and hence are more readily subject to deflection as a result of their own weight and the tension in the dryer felt. For example, felt return roll 25 would probably tend to sag due to the combined felt weight, its own weight, and the tension in the felt. Other felt rolls in the dryer section might tend to deflect in a horizontal plane or even upwardly, depending upon the particular combination of forces acting on them. If the net effect of the deflection of all rolls were to cause greater tension in the felt adjacent the edges thereof than in the center thereof, the felt would tend to press the paper web against the surface of the dryer drum with greater pressure along the edges of the web than towards the center. This would result in a web having a higher moisture content near its center portion than adjacent its edges. Conversely, if tension adjacent the center of the felt is greater than at the edges, the web would be drier in the center than at its edges as it leaves the dryer section.
To compensate for the uneven felt tension caused by deflections of the felt rolls, one of the felt rolls, preferably the last roll immediately upstream of the dryer section, is provided with means for varying the pressure with which it contacts the felt along the length of the roll. In this regard it should be noted that the term dryer section includes not only the series of drums per se, but ancillary equipment such as the intermediate felt rolls 22, 32. As seen in FIG. 2, the variable pressure means may take the form of apparatus for causing the roll, such as roll 24 or 34, to deflect relative to its axis in the desired direction. Thus as seen in FIG. 2, the roll 24 may be mounted on a rigid supporting beam 40 having a pair of fixed, self-aligning bearings 41 mounted thereon and rotatably receiving the journals 42 protruding from each end of the roll 24. At the outer ends of the journals 42 are movable bearings 43, which are also preferably of the self-aligning type, and which have depending therefrom the adjusting mechanisms 44. A bracket member 45 is rigidly attached to each end of the beam 40 and protrudes outwardly therefrom to engage the adjusting mechainsms 44.
From the above, it will be apparent that by means of the adjusting mechanisms 44, the movable bearings 43 may be moved in a direction normal to the axis of the roll 24. This will cause the journals 42 to pivot about the fixed bearings 41 and in turn, cause the center of the roll 24 to bow upwardly or downwardly, as indicated at 46 and 47 in FIG. 2.
When the tension in the felts is nonuniform in the cross machine direction, this may be readily noted by observing the dryer felt seam as it passes through the dryer section. Thus as seen in FIG. 3, if the dryer felt seam is observed to be "leading" or bowed in the direction of travel, as indicated by the phantom line 50, this would be an indication that the tension in the center of the felt is greater than that at the edges of the felt, and the machine operator could compensate for this condition by imparting a reverse crown to the roll 24 by means of the adjusting mechanism 44. Conversely, if the dryer felt is "lagging", that is, bowed away from the direction of travel of the felt as shown by phantom line 51, the machine operator could impart a positive crown to the roll 24 to correct for this condition. When the net deflection of all of the dryer felt rolls is compensated for by the roll 24, the dryer felt seam will return to a position substantially normal to the direction of travel as shown at 52 in FIG. 3.
From the above, it will be apparent that through deflection compensation by means of the variable crown rolls 24 and 34 nonuniform felt tensions may be substantially alleviated, and a uniform moisture profile obtained in the paper web as it leaves the dryer section.
While the form of apparatus herein described constitutes a preferred embodiment of the invention, it is to be understood that the invention is not limited to this precise form of apparatus, and that changes may be made therein without departing from the scope of the invention.
Conventional practice in drying a web of newly formed paper is to convey the moisture-laden web through a series of presses where water is expressed from the web by pairs of pressure rolls, and then to pass the web through a dryer section comprised of a series of large diameter, steam-heated drums. The drums in the dryer section are generally arranged in two sets, with the axes of the drums of each set oriented in generally the same horizontal plane. The drums in one set are positioned beneath the drums in the other set with their axes offset with respect to the set above them, and the paper web is trained in serpentine fashion about the drums. In this manner the paper web is pressed against the surfaces of each of the heated drums and is in turn heated, causing moisture to be evaporated from the web.
To enhance the drying rate, an endless felt is usually associated with each set of drums to press the wet web against the surface of the drums. To some extent, the pressure with which the felt presses the wet web against the drum surfaces will determine the rate at which the web is dried. It will also be obvious that if the tension in the dryer felt is nonuniform in the cross machine direction, the pressure with which the wet web is pressed against the drum surfaces will also be nonuniform and result in a nonuniform moisture profile in the web.
SUMMARY OF THE INVENTION
It has been discovered that a major cause of uneven felt tension in the cross machine direction the deflection of the rolls guiding the dryer felt about the surfaces of the dryer drums. To compensate for deflection of the dryer felt rolls, the present invention provides means for varying the tension in the dryer felt in the cross machine direction by varying the pressure with which at least one of the dryer felt rolls bears against the inner surface of the felt. This is accomplished by flexing the roll relative to its axis.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a somewhat schematic view of a dryer section of a paper machine incorporating the present invention;
FIG. 2 is an elevational view with parts in section showing a variable crown roll which finds utility in the present invention; and
FIG. 3 is a plan view of a portion of the dryer felt showing the effect on the dryer felt seam of varying tension transversely of the felt.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
As seen in FIG. 1 of the drawings, a web of paper W, shown in phantom lines, is led from the last press 10 of a press section about a pair of rollers 11 and 12, and thence into the dryer section comprising a plurality of additional rollers and referenced in its entirety by the numeral 13. The dryer section 13 comprises an upper set 20 and a lower set 30 of large diameter, steam-heated drums with the axes of the drums of each set in substantially the same horizontal plane and with the axes of the drums in the lower set offset with respect to the axes of those in the upper set. In this way, as the web enters the dryer section, it may be trained around each of the drums in serpentine fashion. To press the web W against the surfaces of the drums and to enhance heat transfer from the drums to the web, and hence the drying rate, a pair of endless felts 21 and 31 are provided, one for each set of drums in the dryer section.
The lower run of the upper felt 21 is maintained adjacent a portion of the peripheries of the upper set of drums 20 by means of a series of intermediate felt rolls 22, while lower felt 31 is maintained in position by means of the intermediate felt rolls 32. As the felts 21 and 31 leave the last drum in their respective sets, they are conveyed by means of turning rolls 23 and 33, respectively, a series of guide and stretch rolls, and lead in rolls 24 and 34, respectively, back into the dryer section.
As will be observed from FIG. 1, the felt rolls are of considerably less diameter than the dryer drums, and hence are more readily subject to deflection as a result of their own weight and the tension in the dryer felt. For example, felt return roll 25 would probably tend to sag due to the combined felt weight, its own weight, and the tension in the felt. Other felt rolls in the dryer section might tend to deflect in a horizontal plane or even upwardly, depending upon the particular combination of forces acting on them. If the net effect of the deflection of all rolls were to cause greater tension in the felt adjacent the edges thereof than in the center thereof, the felt would tend to press the paper web against the surface of the dryer drum with greater pressure along the edges of the web than towards the center. This would result in a web having a higher moisture content near its center portion than adjacent its edges. Conversely, if tension adjacent the center of the felt is greater than at the edges, the web would be drier in the center than at its edges as it leaves the dryer section.
To compensate for the uneven felt tension caused by deflections of the felt rolls, one of the felt rolls, preferably the last roll immediately upstream of the dryer section, is provided with means for varying the pressure with which it contacts the felt along the length of the roll. In this regard it should be noted that the term dryer section includes not only the series of drums per se, but ancillary equipment such as the intermediate felt rolls 22, 32. As seen in FIG. 2, the variable pressure means may take the form of apparatus for causing the roll, such as roll 24 or 34, to deflect relative to its axis in the desired direction. Thus as seen in FIG. 2, the roll 24 may be mounted on a rigid supporting beam 40 having a pair of fixed, self-aligning bearings 41 mounted thereon and rotatably receiving the journals 42 protruding from each end of the roll 24. At the outer ends of the journals 42 are movable bearings 43, which are also preferably of the self-aligning type, and which have depending therefrom the adjusting mechanisms 44. A bracket member 45 is rigidly attached to each end of the beam 40 and protrudes outwardly therefrom to engage the adjusting mechainsms 44.
From the above, it will be apparent that by means of the adjusting mechanisms 44, the movable bearings 43 may be moved in a direction normal to the axis of the roll 24. This will cause the journals 42 to pivot about the fixed bearings 41 and in turn, cause the center of the roll 24 to bow upwardly or downwardly, as indicated at 46 and 47 in FIG. 2.
When the tension in the felts is nonuniform in the cross machine direction, this may be readily noted by observing the dryer felt seam as it passes through the dryer section. Thus as seen in FIG. 3, if the dryer felt seam is observed to be "leading" or bowed in the direction of travel, as indicated by the phantom line 50, this would be an indication that the tension in the center of the felt is greater than that at the edges of the felt, and the machine operator could compensate for this condition by imparting a reverse crown to the roll 24 by means of the adjusting mechanism 44. Conversely, if the dryer felt is "lagging", that is, bowed away from the direction of travel of the felt as shown by phantom line 51, the machine operator could impart a positive crown to the roll 24 to correct for this condition. When the net deflection of all of the dryer felt rolls is compensated for by the roll 24, the dryer felt seam will return to a position substantially normal to the direction of travel as shown at 52 in FIG. 3.
From the above, it will be apparent that through deflection compensation by means of the variable crown rolls 24 and 34 nonuniform felt tensions may be substantially alleviated, and a uniform moisture profile obtained in the paper web as it leaves the dryer section.
While the form of apparatus herein described constitutes a preferred embodiment of the invention, it is to be understood that the invention is not limited to this precise form of apparatus, and that changes may be made therein without departing from the scope of the invention.